DESCRIPTION: (Scanned from the applicant's description): The ductus arteriosus (DA) is dilated in the hypoxic environment of the developing fetus. At birth the DA constricts in response to normoxia. In contrast, the pulmonary artery (PA) is dilated in normoxia and constricts in hypoxia. Although their responses to 02 are opposite, both vascular tissues have 02-sensitive K* channels expressed in their smooth muscle cells (SMC). In the DA, normoxia inhibits a K* channel to cause constriction, while in the PA hypoxia inhibits a similar channel. The mechanism by which these channels sense changes in 02 is unknown. It is hypothesized that: 1. A rise in 02 increases production of reactive 02 species in both the DA and the PA 2. A rise in 02 increases the levels of oxidized, cytosolic, redox couples in both the DA and PA. 3. An oxidized cytosol associated with normoxia, inhibits K channel activity in the DA SMC, resulting in membrane depolarization and increasesK channel activity in the PA, causing hyperpolarization. In contrast, a reduced cytosol associated with hypoxia increases K channel activity in DA SMC and inhibits K channel activity in PA SMC. 4. An oxidized cytosol associated with normoxia results in an increase in intracellular Ca2 and vasoconstriction in the DA and a decrease in Ca2i in the PA and vasodilation in the DA and increased [Ca2+]i and vasoconstriction in the PA. These studies will determine whether the different responses of the DA and PA to O2 are due to opposite modulation of K+ channel activity by the same cytosolic redox changes. Changes in O2 species and redox couples will be measured using chemiluminescence and 2', 7'-dichlorofluorescein and Amplex Red fluorescence. The effect of changing the redox status of the cytosol on K+ channel activity and membrane potential will be determined using patch-clamp techniques. Changes in [Ca2+]i in response to altering the redox status of the cell will be recorded using single-cell Ca2+ imaging techniques in combination with patch-clamping, while redox-mediated changes in tone will be determined in isolated DA and PA rings and whole rabbit lungs. Persistent patent ductus is a common congenital defect in newborns and treatment of pulmonary hypertension is extremely limited. An understanding of the mechanisms of O2-mediated changes in tone in the DA and PA would therefore be of significant medical importance.